WASHINGTON — With the threat of a government shutdown just days away, an urgent message filled e-mail inboxes around the country late last week: Top Senate Republicans, the message said, were committing “the ultimate betrayal.”

Senate minority leader Mitch McConnell refused to filibuster a government funding bill pushed by Democrats, and other establishment GOP senators also would not block the measure.

“These Senate leaders have surrendered,” read the note from the Senate Conservatives Fund, an outside political group operated by former South Carolina senator Jim DeMint, an influential Tea Party conservative.

The aggressive tactics employed by the Senate Conservatives Fund and other conservative political groups are placing immense pressure on Republicans in Congress, and they are one reason they have chosen a course of action that resulted in government shutdown rather than abandon their demands that the new health care law be killed or weakened.

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By sowing fear among more mainstream conservatives — who might otherwise be willing to cut a deal to end gridlock — these combative appeals greatly amplify the potency of Tea Party hard-liners in Congress, who number
about 35 of the 232 Republicans in the House and just a handful of the GOP Senate minority.

If they choose to defy these groups, many Republicans would face aggressive primary challenges and conservative backlash at home.

The message is delivered via broadcast and online advertising, e-mail campaigns, websites, and grassroots organizing. Borrowing a tactic from Grover Norquist’s Americans for Tax Reform, which asks candidates to sign a no-tax-increase pledge, the Senate Conservatives Fund also is asking all 2014 candidates to sign a broadly worded pledge to never vote for a bill that provides funding to implement any part of President Obama’s health care law.

“Tell the Republicans to stop capitulating,” the group wrote on its website.

Among the senators in its crosshairs are Kelly Ayotte of New Hampshire and Susan Collins of Maine, who have both urged compromise over the government shutdown. They have warned the hard-liners in their party that now is not the right time for a health care fight.

“I will say to my Republican colleagues in the House and to some in this chamber, it’s time for a reality check,” Ayotte despaired on the Senate floor on Friday.

During the last government shutdown, nearly two decades ago, 79 of the 236 House Republicans were in vulnerable swing districts that Bill Clinton had won in the previous election, according to David Wasserman, who studies House elections for the Cook Political Report. Now, 17 of the 232 House Republicans represent districts Obama won last year.

That means Republicans generally need not worry about a Democratic challenger, but they do have to think about a Republican one, in a primary — where the most extreme conservatives often win.

The Club for Growth, a nonprofit political advocacy group, has been among the most active in fielding conservative primary challengers in recent elections, and has the best track record. Many of the arch-conservative lawmakers now in office were elected with the group’s help.

“The short answer is: We watch,” said Chris Chocola, president of the Club for Growth. “Our guys are doing the right thing. What we’re doing is trying to find . . . reinforcements.’’

For example, the Club for Growth earlier announced it was supporting a challenger to Representative Mike Simpson, an eight-term Republican from Idaho. Simpson, an ally of House Speaker John Boehner, has said he would support a budget bill that isn’t tied to defunding the health care law.

“There is an old saying in politics that you never want to take a hostage that you can’t shoot,” he told the Idaho Statesman in August. “This is a hostage we should not shoot, and I won’t. Closing the government down has significant consequences.”

His challenger, Tea Party-backed Bryan Smith, has criticized Simpson for that stance. Simpson did not respond to requests for comment on Friday.

The most aggressive push has come from DeMint, who used to lobby his colleagues from inside the Senate but is now attempting to pressure them from outside. In April, he took over the Heritage Foundation, a conservative think tank, and is now using its political arm, Heritage Action, as a powerful conservative weapon, along with his Senate Conservatives Fund.

Dan Holler, communications director for Heritage Action, said the group began laying the groundwork months ago for the current fight over the shutdown. They staged a nine-city town hall tour across the country, holding rallies for those who want to defund the health care law. During a summer break for Congress, they encouraged supporters to show up at town hall meetings.

They ran digital ads in 100 Republican districts, encouraging members to vote against funding the law.

“The strategy behind this whole thing was to get Republicans on board with defunding,” Holler said. “The House came back after their five-week recess, they heard from their constituents, and they acted accordingly.”

In recent days, they have focused on pressuring Democrats in conservative states, announcing a $400,000 ad buy.

DeMint’s Senate Conservatives Fund raised $1.5 million in August alone. But so far this year it has not spent any of its money supporting a Senate candidate — it has spent most of its money against Senate Republicans it opposes.

“Jeff Flake used to be one of us,” an online ad posted Aug. 26 says, referring to a newly elected senator from Arizona. “But now he’s become one of them.”

Flake, when asked Friday what he makes of the influence of outside groups, let out a chuckle.

“I don’t know. I don’t want to say anything on the record,” he said. “It is what it is. You deal with it.” Then, in a subtle dig about failures to defund the health care law, he added, “The bottom line is, if you’re going to take a stand . . . do it on something you can win.”

Senate Conservatives Fund also started a website, dontfundobamacare.com, that targets certain Republican senators. Several — including Collins; Thad Cochran of Mississippi; Lindsey Graham of South Carolina; John Cornyn of Texas; and Lamar Alexander of Tennessee — have not signed the pledge to oppose any bill or budget that provides funds for the national health insurance expansion.

“As a policy, Senator Collins does not sign pledges,” said Jeremy Kirkpatrick, a spokesman for Collins. “She pledges allegiance to the flag and to uphold our Constitution; she does not sign pledges of special interest groups.”

He also criticized a group “that is not from Maine” for trying to suggest her vote to move forward on a budget bill meant she supports Obama’s health care law.

“Despite her strong opposition to Obamacare, she disagrees with the unrealistic strategy, pursued by some Republicans, of linking Obamacare to the funding of the entire government,” Kirkpatrick said.

McConnell, who has a Tea Party-backed primary challenger, also has not signed the pledge. His opponent, Matt Bevin, has. And the Senate Conservatives Fund recently warned that it would consider backing Bevin over McConnell in the race. That threat has inhibited McConnell’s deal-making abilities.

The group’s aggressive tactics have come under fire from Senate Republicans, who have been particularly angry at Senator Ted Cruz, a Republican from Texas who has been treated like a hero by the Senate Conservatives Fund.

Cruz has declined calls to distance himself from the group, and when approached on Friday he downplayed their influence.

“A lot of Washington politicians are obsessed with outside groups,” Cruz said. “I think the credit for the national debate we have had over the past several weeks on all the harms Obama
care is causing — I think the credit lies with the American people. It’s not with any group.”

But as talk begins to move toward the possibility of a so-called grand bargain, the groups are already issuing warnings.

“We are urging caution about moving away from the Obamacare stuff to a grand bargain,” Holler said. “If they do anything short of defund Obamacare, it’s going to be really tough to go back home and explain why that vote is cast.”

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